Modern automotive engines typically rely on numerous engine parameters for correct engine operation. Optimum engine parameters are generally stored in the memory of an engine controller. Sensors on the engine are used to sense actual engine parameters while the controller compares these sensed values to the stored optimum valves. As a result, it is important that a reliable, repeatable sensor be installed in the engine having little engine-to-engine variation, such that a correct engine operating parameter is sensed.
Various sensors for sensing the temperature of a rigid body, such as a cylinder head of an internal combustion engine, have been developed. The sensor must be in intimate thermal contact with the rigid body to sense the proper temperature. To provide good thermal conductivity, some sensor designs utilize a conductive paste applied on the exterior of the sensor. Other sensor designs utilize a spring such that, when installed, the spring provides a force to bias the sensor into contact with the rigid body to establish adequate thermal conductivity. Still other sensor designs rely on the mounting threads to provide the conductive path between the rigid body and the sensor.
The inventors of the present invention have recognized disadvantages with these prior art sensors. For example, in addition to being more costly sensor assemblies, variations in sensed temperature may result. In the spring loaded sensor design, manufacturing variations in the spring itself or deterioration of the spring rate over time may cause a change in the spring force, thereby causing a variation in sensed temperature. In the case of using a thermally conductive paste on the exterior of the sensor, the paste may migrate from the desired location or may degrade over time. A disadvantage with the sensors that rely on the mounting threads as the conductive path is that the sensors are generally unreliable due to manufacturing variations. In addition, packaging issues arise. Generally, the space in the cylinder head near the combustion chamber for mounting the sensor is limited and thus providing receiving threads at this location may not be practical.